1. Field of the Invention
The present invention relates to a planographic printing plate. More particularly, the present invention relates to a planographic printing plate which can effect developing with water or directly producing a printing plate by operating an infrared laser according to digital signals without developing.
2. Description of the Related Art
Conventionally, various methods have been known for producing a printing plate directly from digitalized image data via no lith film, for example, (1) a method using an electrophotographic method; (2) a method using a highly sensitive photopolymer which can be inscribed by a laser having relatively low output which emits blue or green light; (3) a method using a silver salt or a complex system of a silver salt with other system, and (4) a method in which an acid is generated by exposure to a heat mode laser and a thermoset image is obtained by post-heating using the acid as a catalyst.
Though these methods are extremely useful for simplifying a printing process, they are not necessarily fully satisfactory. For example, the method (1) using an electrophotographic method is complicated in image forming processes such as charging, exposure, developing and the like, and the apparatus used for this method is complicated and large in scale. In the method (2) using a photopolymer, handling in bright room is difficult since the printing plate has high sensitivity. In the method (3) using a silver salt, there are some defects in that the treatment is complicated, silver is included in a treatment waste solution, and the like. The method (4) is also complicated since post-heating and developing treatment thereafter are necessary.
Further, the production method for these printing plates include, after the exposure process, a wet developing process for removing a recording layer made on the surface of a substrate to leave an image-wise concave, and a post-treating process in which a developed printing plate is washed with washing-water and treated with a rinse solution containing a surfactant and a desensitizing solution containing gum arabic and a starch derivative.
On the other hand, in recent plate producing and printing arts, environmental problems are noticed since development waste solutions exhibit an alkaline character. Further, simplification of plate production works have been developed. There is a need for a printing plate which does not require the complicated wet developing treatment as described above and can be used for printing after exposure without any treatment.
Regarding the printing plate which does not require developing treatment after exposure of an image, for example, U.S. Pat. No. 5,258,263 which discloses a planographic printing plate which is formed by laminating a photosensitive hydrophobic layer and a photosensitive hydrophilic layer on a substrate, of which curing or insolubilizing is promoted in an exposed range. However, this plate is a printing plate of so-called on-printer-developing type in which a unexposed part of a photosensitive layer is removed during a printing process, and has the defect that it pollutes wetting water and printing ink. Further, in this plate, adhesion between the photosensitive hydrophilic layer and the photosensitive hydrophobic layer is problematical due to its two-layer structure, and there is a defect that a lot of prints can not be printed.
As a planographic printing plate which does not require wet developing treatment after formation of an image, there are disclosed printing plates having a silicone layer and a laser heat sensitive layer below the layer in U.S. Pat. Nos. 5,353,705 and 5,379,698. Although these plates do not require wet developing, they have the defect that rubbing and treatment with a special roller are necessary for completing removal of the silicone layer by laser abrasion, and the treatment is complicated.
There is disclosed a system in which a film obtained by sulfonation of polyolefins is used, and hydrophilicity of the surface thereof is changed by thermal inscription to form a planographic printing plate which does not require developing treatment in Japanese Patent Application Laid-Open (JP-A) Nos. 5-77,574, 4-125,189 and 62-195,646 and U.S. Pat. No. 5,187,047. In this system, a sulfonic group on the printing plate is de-sulfonated by thermal inscription to form an image. Thus developing treatment is not required, however, there is a defect that a harmful gas is generated in the thermal inscription.
U.S. Pat. Nos. 5,102,771 and 5,225,316 suggest a planographic printing plate obtained by combining a photo acid-generating agent with a polymer carrying an acid sensitive group on a side chain, namely a no-developing system. This planographic plate has a defect that it has only limited hydrophilicity since the acid generated is a carboxylic acid and consequently, is poor in durability of the plate and brightness of the printed image.
JP-A No. 7-186,562 (EP 652,483) discloses a planographic printing plate containing an infrared absorbing pigment and a polymer which generates a carboxylic acid by action of heat and acid. However, a planographic plate using this planographic printing plate has a problem that stain is made in printing.